The invention relates to safety appliances, and more particularly pertains to a device for draining a tank of hazardous fluid in an emergency.
In the handling, transit, storage and use of hazardous fluid materials contained in tanks, an emergency may arise making it necessary or prudent to evacuate the tank even though the normal discharge apparatus is incapacitated, inaccessible or otherwise unavailable. In particular, over-the-road transport of potentially hazardous fluids such as gasoline in tank trucks may result in such an emergency. When a mishap occurs leaving a tank truck overturned, for example, it is an accepted safety practice to first drain the tank before other salvage operations are attempted. Where normal discharge apparatus has been disabled by damage or inverted orientation or made inaccessible by surrounding obstacles, one prior manner of draining the tank was to drill a hole with special equipment at an appropriate point in the tank and then draw off the hazardous fluid through a suction line. This procedure involved a degree of risk because possible sparks and overheating of the drill could result in an explosion or ignition of the product carried in the tank. Furthermore, the special equipment necessary to perform this procedure is relatively expensive and as a result is often not immediately available at an accident site.
Another prior procedure to evacuate an overturned tank truck involves special apparatus which is assembled over the manhole weld collar on the tank. The apparatus incorporates rubber gloves through which the manhole can be operated for access and draining of the tank through the manhole and the apparatus. Problems of leakage with the seal between the apparatus and the manhole structure are often encountered. These leakage problems cannot be readily avoided because of variations in shape and size of the manhole weld collars and other structural elements of the manholes. Another problem with known emergency evacuation techniques such as those involving access through a manhole is that there is ordinarily no provision for controlling or limiting the vacuum developed in a tank as it is evacuated of product. Excessive vacuum buildup inside a tank can result in its collapse and such damage can readily exceed that which might have occurred in the original mishap.